Given that we need to choose 4 books out of available 10 different books,

Let us assume the choosing the no. of ways be N,

⇒ N = choosing 4 books out of 10 books

⇒ N = ¹⁰C₄

We know that

And also n! = (n)(n – 1)(n – 2)…………2.1

⇒

⇒

⇒

⇒ N = 210 ways